Those K series are some real speakers, as opposed to those pressed-frame speakers that everyone uses. The die cast frame has no flex and no ringing when you tap it with a screwdriver. That alnico magnet is very powerful, but there is practically no magnetism outside of it. The edgewound aluminum voice coil gets almost all of the magnetic field. The frequency response is way far and away the flattest for any guitar speaker I have ever owned. And loud. I used to play through a pair of K130's that would dominate anybody's Marshall rig. But, for the past twenty years or so, I have played through Marshall cabinets with Celestion G12T-75's. Because that is the "sound of Rock".
I use three different speakers when testing new circuits. I will use the G12T-75 if it is a Rock or Metal circuit, a Fender 12" out of a twin if it is a Fenderish circuit, and I will use a K120 if I want to know what it really sounds like.
I play bass through four JBL Ki40's and all four have been reconed somewhere along the line. A buddy of mine burned-up a pair early on when he turned the compressor off and played some funk. I called up JBL and somebody answered the phone (it was different days). I sent them the speakers and, for a fee, they reconed them good as new. More recently, I had the other pair reconed in Sacramento or somewhere with an cheap after market cone and it rendered them quite inferior to the original.
The K120 is an exceptional speaker and I would encourage you to seek out a reputable firm that has a quality edgewound replacement and the ability to install it correctly.